v2.4.0.8

Investments - Credit Ratings (Details) (USD $) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2013 | Sep. 30, 2012 | Sep. 30, 2013 | Sep. 30, 2012 | Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |
OTTI | $ 0 |  | $ 0 | $ 0 |  | $ 0 |  |
Amortized cost | 2,620,107,000 |  |  | 2,620,107,000 |  |  | 2,475,202,000 |
Fair value | 2,674,305,000 |  |  | 2,674,305,000 |  |  | 2,618,697,000 |
% of Total fair value | 100.00% |  |  | 100.00% |  |  | 100.00% |
U.S. treasury bonds [Member] |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |
Amortized cost | 16,629,000 | [1] |  | 16,629,000 | [1] |  | 42,671,000 | [1]
Fair value | 17,374,000 | [1] |  | 17,374,000 | [1] |  | 43,931,000 | [1]
% of Total fair value | 0.70% | [1] |  | 0.70% | [1] |  | 1.70% | [1]
U.S. agency bonds [Member] |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |
Amortized cost | 1,146,065,000 | [1] |  | 1,146,065,000 | [1] |  | 974,331,000 | [1]
Fair value | 1,139,011,000 | [1] |  | 1,139,011,000 | [1] |  | 1,005,263,000 | [1]
% of Total fair value | 42.60% | [1] |  | 42.60% | [1] |  | 38.40% | [1]
AAA [Member] |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |
Amortized cost | 153,544,000 | [1] |  | 153,544,000 | [1] |  | 171,136,000 | [1]
Fair value | 165,945,000 | [1] |  | 165,945,000 | [1] |  | 183,950,000 | [1]
% of Total fair value | 6.20% | [1] |  | 6.20% | [1] |  | 7.00% | [1]
AA Plus, AA, AA Minus [Member] |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |
Amortized cost | 114,209,000 | [1] |  | 114,209,000 | [1] |  | 186,495,000 | [1]
Fair value | 121,167,000 | [1] |  | 121,167,000 | [1] |  | 196,797,000 | [1]
% of Total fair value | 4.50% | [1] |  | 4.50% | [1] |  | 7.50% | [1]
A Plus, A, A Minus [Member] |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |
Amortized cost | 487,189,000 | [1] |  | 487,189,000 | [1] |  | 477,236,000 | [1]
Fair value | 517,408,000 | [1] |  | 517,408,000 | [1] |  | 515,383,000 | [1]
% of Total fair value | 19.30% | [1] |  | 19.30% | [1] |  | 19.70% | [1]
BBB Plus, BBB, BBB Minus [Member] |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |
Amortized cost | 646,396,000 | [1] |  | 646,396,000 | [1] |  | 587,858,000 | [1]
Fair value | 658,567,000 | [1] |  | 658,567,000 | [1] |  | 637,089,000 | [1]
% of Total fair value | 24.60% | [1] |  | 24.60% | [1] |  | 24.30% | [1]
BB Plus or Lower [Member] |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |
Amortized cost | 56,075,000 | [1] |  | 56,075,000 | [1] |  | 35,475,000 | [1]
Fair value | $ 54,833,000 | [1] |  | $ 54,833,000 | [1] |  | $ 36,284,000 | [1]
% of Total fair value | 2.10% | [1] |  | 2.10% | [1] |  | 1.40% | [1]
[1] | Ratings as assigned by Standard & Poor’s ("S&P")

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- Definition Amount of debt securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -Section 50 -Paragraph 2 -Subparagraph (b)-(g) -URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62557-112803 + Details
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- Definition The change during the reporting period in the cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27340-111563 + Details
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